This research pursues two major objectives: (1) to explore the use of the construct of psychopathy in the diagnosis of antisocial personality disorder (APD), and (2) to evaluate the reliability and validity of two recently developed self-report measures of psychopathy. (1) Heterogeneity of APD. The current DSM-IV criteria for APD have been criticized for lacking an adequate empirical or theoretical basis, and for lumping together subgroups of individuals whose superficial (i.e., symptomatic) similarities mask important etiological differences of a social, constitutional, or psychological nature. We will administer Hare's Psychopathy Checklist - Revised (PCL-R) and measures of variables hypothesized to be associated with the etiology of subtypes of psychopathy to two groups of subjects - adult prison inmates and adults in substance abuse treatment programs. Cluster analyses will be used to identify discrete subgroups within each sample; the groups will be compared on a variety of self-report, laboratory, and behavioral measures to evaluate the theoretical validity and practical utility of the empirically derived clusters. (2) Self-report Measures of Psychopathy. Although Hare's PCL-R is widely regarded as the best measure of psychopathy, it has a number of limitations. Although scales designed to measure APD and/or psychopathic features from conventional personality inventories have historically correlated poorly with the PCL-R, new self-report psychopathy measures that appear to have better content validity may perform better. The psychometric properties, reliability, and construct validity of Levenson's Psychopathy Scales (LPS) and Lilienfeld's Psychopathic Personality Inventory (PPI) will be evaluated in this research.